The need to develop an accurate chair-side screening instrument for caries activity and caries risk has been long recognized and extensive research work has been done in this area without much success. Our study takes a new approach in solving this problem. This approach is founded on a novel model, the Caries Risk Pyramid (CRP), which summarizes the available knowledge regarding the biology of dental caries. HYPOTHESIS: Based on the CRP model, we hypothesize that measuring the ability of dental plaque and/or saliva to generate alkali from urea, or other salivary substrates, together with the ability to generate acid from sugars, can provide an accurate estimation of an individual's caries status and possibly future caries risk because they summarize the combined effect of other caries risk factors. OBJECTIVE: In order to test this hypothesis we have developed an array of novel, chair-side tests for measuring acid and alkali generation in plaque and in saliva. The objective of this study is to assess the reliability and validity of these tests as screening tools for dental caries and to explore possible ways of combining the results of these tests in order to accurately identify individuals with caries. To accomplish this objective, a cross-sectional study on 200 adult subjects is proposed. SIGNIFICANCE: The proposed tests are novel because they consider the ability to generate alkali in plaque as a potential caries risk factor, which has not been previously included in existing multivariate risk assessment models. They are of low cost and give faster results compared to available biological caries risk tests. They do not require dental expertise, which makes them suitable for use by non-dental professionals. Once the tests have been validated in adults, our ultimate goal is to validate them in children and infants as screening tools for Early Childhood Caries (ECC), and ultimately as a predictor of future caries risk, either independently, or in combination with other caries risk factors. Another important potential application for the proposed tests would be the comparison of pre- to post- intervention risk in clinical dental practice, in research, and in community interventions.